Elvis may have permanently left the building 27 years ago, but yesterday he clocked up his 20th UK No 1 single - a re-released 1959 hit, One Night - amid predictions that the singles format is in terminal decline. The king's latest triumph - if that is the word for a CD that managed to top the chart with just 30,000 sales - is also the 1,000th No 1 since the UK chart began in 1952. Low sales or not, the music industry is rolling out a series of promotions to tie in with the milestone.

This is the second time One Night has been Britain's biggest seller. At the time of its first visit, music was a very different industry. Singles were, as now, "shop windows" for higher-priced albums, but turnover at the top of the chart was far slower. Today's short-attention-span culture sees a new No 1 almost every week, spawning the perception that reaching the top is no longer so prestigious.

Knowing what was No 1 each week used to be de rigueur for any adolescent who wanted a social life. Ignorance of the charts marked one as tragically uncool in a time when the weekly Radio 1 countdown was mandatory listening. BBC 6 Music broadcaster Andrew Collins remembers "going home at lunchtime on Tuesday to hear the chart, because it was so important."

Its social importance waned in the late 1990s, as teenagers found other diversions such as computer games, and sales began to drop. Making matters worse was the advent of reality-TV stars such as Pop Idol's Michelle McManus, whose short careers were marked by singles that shot straight to No 1, then straight to oblivion. The rise of internet downloading, and its snazzy iPod hardware, seems to have sealed its fate. Number ones are now perceived by many as irrelevant one-week wonders, and singles sales as a whole have dropped 41% in the last 12 months.

That has not kept the Official Charts Company, which compiles the charts by tracking sales in 6,000 shops, from turning the 1,000th No 1 into an event. The Capital Gold radio network will devote this week to playing all 1,000 songs, Omnibus Publishing is to follow with a book, and Channel Five will air a primetime programme on February 7.

There will soon be no excuse for not knowing that the first No 1 was Here in My Heart by American crooner Al Martino, and for the fact that you aren't alone in not knowing a single one of Westlife's 12 chart-toppers.

Not everybody is in a celebratory mood, however. "It's like the 100th customer through the doors of a supermarket getting a prize," Collins complained. David Steele, whose V2 Records is home to Paul Weller and Stereophonics, was even less enthusiastic. "We shouldn't celebrate anything about the singles chart, because there's nothing to celebrate. People don't buy singles any more. The way it's going, physical singles will be extinct in a few years."

Sales of "physical" singles are at crisis point as consumers desert record shops for their home PCs, where tracks can be downloaded for about 79p each, rather than the £3.99 shop price. Downloading's popularity has been fuelled by the introduction of the iPod, which can store 10,000 downloaded tracks. Its telltale white wires, already trailing out of ears on every city street, are set to become ubiquitous with last week's launch of the lower-priced iPod Shuffle.

This does not bode well for the CD single, as it prepares to join the fax machine and video recorder in a charity shop near you. The business is still pondering the ramifications of a fortnight ago, when another Presley reissue, Jailhouse Rock, be came the 999th No 1 with 21,000 sales - the lowest ever for a chart-topper. Downloads will soon be incorporated into the chart, but even this will not make singles the cultural touchstones they were as recently as 1995, when a Blur v Oasis chart battle made the the evening news.

According to Paul Williams of Music Week magazine, the excitement waned when singles began automatically to enter the chart at No 1 - landed there by ad vance radio play and mailshots to fans - rather than start low and gradually climb. Of the 156 No 1s this century, only three did not debut at the top. "It's all about scheduling now. It's much easier for the business to line up what's going to be No 1 - you know from the schedules, 'Oh, that'll be No 1, and next week that'll be No 1'. In the past, you could never predict - it was all up to the fans."

The Elvis reissues are a prime example of the way releases have been stripped of spontaneity. BMG Records, owners of Presley's back catalogue, has never been reticent about exploiting its goldmine through regular reissues. Seizing another opportunity with the 70th anniversary of his birth on January 8, it began re-releasing all 18 of his previous British chart-toppers, one per week.

Investment

To persuade fans who already owned them to buy them again, it sold a limited-edition box storage box containing the first single, All Shook Up. The box was £10.99, and it will cost another £68 to stock it fully. "People have invested in the box, and they'll want to fill it," said Gennaro Castaldo of retailers HMV, which has sold out of the box. "He should have consistent Top 5s until April."

Released last week as a limited run of 30,000 and helped along by the publicity surrounding the 1,000th No 1, One Night easily outsold the second-biggest seller, the Manic Street Preachers' new single. The manipulation irks Collins. "The moral victory was the Manics'. They're the spiritual number one."

Well, 30,000 Elvis fans would disagree (and those who missed buying a box can bid for one, starting at £45, on auction website eBay). In a way, though, the dedicated 30,000 are getting off lightly, because BMG originally planned to re-release all his US and UK number ones - 30 in total.

Meanwhile, it is safe to assume that we will see a lot more of the man from Memphis in next year or two, before some of his biggest hits go out of copyright. BMG's 50-year copyright on classics such as Heartbreak Hotel, Hound Dog, and Blue Suede Shoes expires in 2006, when any label will be entitled to release them without paying BMG a penny.

But, as the king probably wouldn't have said, what's millions of pounds in royalties between friends?